Edith clabke



Sept. 6, 1927.

1,641,737 E. CLARKE ELECTRICAL POWER TRANSMISSION Filed April 50, 1925 HIGHLY SATURATED FIELD PDLES 1- HIGHLY SATUIMTKD [FIELD WLES i'li F f Dv l 6' I o .v, g i is z v 6 '5 Q Q l g 1 I a 1 t 1 l k I E I "5 1 m l I El E 3 S a S t w I THOUSAND KW- AT RECEIVE/i Inventor" Her Attcirne g Patented Sept. 6, 1927.

UNITED STATES BCHENECTADY, NEW YORK, ASBIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

EDITH CLARKE, 01

PATENT OFFICE.

ELECTRICAL POWER TRANSMISSION,

Application fled April 30, 1925. Serial No. 27,047.

reactance of a long line which introduces a considerable drop in voltage under load and a considerable rise in voltage at the receiving end under no load due to chargmg current flowing through the line. In gen- .eral, with any length of line in which the amperes of charging current approach in .magnitude the value of the load current.

the matter of ower factor becomes important, not mere y as one of the underlying features in drop calculatlons but serving as the onl feasible means of controlling voltage an efficiency. 1

Synchronous phase modifiers, such as synchronous condensers, have been used heretofore for correcting the power factor and for regulating and stabilizing the voltage of transmission lines. For example, when the line is carrying a large load wlth a low power factor the condenser 1s overexcited enough to produce a leadmg current large enough ,to counteract 1n part. the inducti e reactive component of the line drop. When the line is carrying a small load, the synchronous condenser is underexcited so that it draws a lagging current suflicient to maintain a line drop between the generator and receiving circuit equal to the full load line drop.

The change in excitation necessary to vary the reactive power added to the system by a synchronous phase modifier is usually accomplished by means of a vibratory type of regulator periodically short clrculting a series resistance in the field of the exciter for the phase modifier, the regulator being responsive to line voltage. ThlS change 1 n excitation, however, occurs at an appreciable interval of time after the applicatlon of load and consequent line voltage change. When the line is operating near the maximum'power limit any decrease in line voltage permitted must be kept small, otherwise the line becomes unstab e upon a suddenly increased power deman Therefore, it bepower limit.

comes important to hold up the line voltage and prohibit a decrease in voltage to a point of instability during whatever interval may be required for the regulator to function to restore the voltage to normal value.

When using synchronous hase modifiers having the characteristics 0 those hitherto used, the margin between the operating load and the maximum power limit must be substantial because of the deficiency in inherent regulating capacity of such phase modifying devices to hold up the line voltage until the regulator functions for sudden changes in load. With long lines it becomes desirable to decrease this margin in order to transmit suflicient power for an. economic development and it becomes important to have a line that is stable near its maximum As will be set forth-more in detail hereinafter, I have devised an electrical power transmission system in which the limitations for power transfer due to voltage variations in the line have been minimized" by suitable design, location, and novel inherent operation of the apparatus comprising the system.

An embodiment of my invention comprises an electrical power transmission system having a source of alternating-current energy supply of synchronous generators, supplying a distant receiving station which may consist of synchronous motors, induction motors, lighting loads, and in general any customary industrial load. The system also comprises highly saturated synchronous phase modifying devices such as synchronous condensers, connected for example at the receiving station and at suitable points along the transmission line connecting the two stations. The synchronous condensers are provided with suitable regulating means, which may, for example, operate similarly to those previously used.

In an electrical power transmission system the line voltage will tend to fall with increased load and in lines operating near the maximum power limit a point of instability is soon reached. Hitherto lines have been operated so that a considerable momentary decrease in line voltage was permissible because the margin maintained between the operating load and the maximum power limit was such that the regulators operated so that the change in condenser excitation and consequent inter-change of to brin the voltage back to a predetermined value efore a point of instability was reached. In the present system the synchronous condensers are so designed and Operated that upon a sudden. ap l1cat1on of load an interchange ofcorrectlve reactive power of sufiicient magnitude-is inherently reactiv%power to the' system was suflicient obtained to prevent the -linevoltage from voltage back to normal and maintain it at such value. I

My invention will be better understood from the following description taken in con-' nection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 is a diagrammatlc illustration of an electrical power transm ssion system embodying my invention; Fig. 2 is a diagram of saturation curves and phase characteristic curves of a normallydesigned synchronous condenser and comparative curves for a synchronous condenser employed in the transmission system embodying my invention; Fig. 3, is a diagram of power-stability curves illustrating in a" general way the improvement in power transmission obtained b my invention.

Referring to Fig.11 o the drawing, 1\ denotes an alternating current generator with an-exciter 3 exciting the field winding 2 of the generator. The apparatus at the generating end provides the energy to be transmitted over step-up transformer 4, the transmission line 5 and the step-down transformer 6 to the receiving station. The re-' ceiving station feedsany general industrial load and includes a synchronous phase advancer 7 such as a synchronous motor or condenser with highly saturated field poles. At

the mid-point of the line, or any other inter-.- mediate point or points between the generator and receiving end, a sim lar synchro-"f nous regulating means such as a synchronous condenser 8 with highly saturated .lfield poles is connected to the line by means ofa sultable transformer 9.

A Tirrill-type or vibratory regulator 11,-

or any similarly sensitive typ'e 0 re ator serves to influence the voltage of exciter 13, which in turn energizes the field winding 12 of synchronous condenser 7. In like manner regulator 14, similar to regulator 11,

influences the voltage (g exciterd 16, which e eld win ing .15 ofin turn energizes/t synchronous condenser 8. The regulators are provided for automaticallyv regulating reater is the reactive power correcv the under-excitation or over-excitation of each synchronous machine as the line voltage changes.

Fig. 2 shows saturation curves for two synchronous condensers as plotted between per cent field amperes and per cent armature volts. Curve A is. for an ordinary synchronous condenser and curve B for a synchronous condenser as used in carrying out my invention. The phase characteristics are represented by curves C, D, E and F, plotted between per cent field am eres and er cent armature amperes. It will be note that for a iven change in line voltage at constant eldcurrent there will be available a greater change of armature current when using the saturated machine. For example, if the curves C and D, and-E and. F, represent phase characteristics at 100% and 95% normal line volta e respectively, a drop in line voltage of 5% ior an'ordinar I machineas indicated by curves C and makes available an increase of about 8% armature amperes at an excitation correspondmg to 100% of that required for full load kilovolt-amperes zero power.- factor leading. However, with a highly saturated machine as represented by curves D and F a change in line volta e of 5% will make available an increase 0 about 30% armatureamperes at the same excitation. It therefore follows that the machine with the" flatter saturation .curve will be capable of 1 supplying a greater amount of reactive kilo-r volt-amperes fora given change in line voltage.

Stability or power-limit curves are shown 1n Flg. 3. These curves consist of plots of voltage agalnst power for synchronous terminal apparatus interconnected by a trans-H05 mission line with field excitation as a parameter. The point of vertical tangency on. each curve marks the maximum power which can be transmitted between the two machines ata given field excitation. A series of such 6 curves will give, at their points of vertical tangency, the power limit for the particular values of excitation for which they are" drawn, and if the locus of these power limit points is drawn, its intersection with any particular constant voltage line will give the maximum power transferable over the line atthat particular voltage. Curve G represents the. power-limit curve of a single cir-. cuit three phase line, 250 miles long with a supply voltage. of 220,000 volts, supplying a load of unity power factor. I The point of vertical tangency to the curve.

1G marks the maximum power which can be transmitted over the assumed line with gen- 12 crating and phase modifying apparatus, of usual design at a given excitation. If an increased load demand occurs suddenly, before the regulator can increase the-field'of the phase modifying device, the voltage will 1 0 fall the system will thn be operating on the underside of the curve or'in a region of instability.

.By using highly saturated phase modlfying devices connected to the s stem the nose of the curve G is extended an takes the new position as represented by the dotted curve H. The same load, assumed as the maximum in the, first instance, may now be car ried, since a small drop in voltage is per-' missible before the point of vertical tangency is reached. Greater loads may be carried with gradually decreasing margins between the operating load and the maximum power limit until the condition of operation is reached as indicated by dotted curve I, which indicates a condition originally encountered with curve G but with a decided increase in the maximum power limit.

The operation of the present system consists generally in shifting the phase position of the line current to be more nearly in phase with the volta e in order to improve the power factor 0% the line and also to maintain a certain desired voltage at the receiving end or along the line. The synchronous condensers 7 and 8 are provided to vary the phase angle at the receiving circuit or along the line by causing the condensers to draw lagging or leading currents and thereby add reactive ower to the system.

The a dition of reactive power in the present system occurs in two steps. First, by the inherent regulating action of the syn chronous condensers and, second, by the change in field excitation effected by regulators 11 and 14 influencing the voltage of the condenser field exciters 13 and 16 respectively.

By inherent regulating action is meant the automatic tendency of a synchronous condenser to draw lagging or leading current depending on the relative values of impressed voltage and the induced or counter voltage of the condenser.- If the impressed voltage drops below the value of the countervoltage, the condenser will draw a leading current. If the impressed voltage rises above the countervoltage the motor will draw a lagging current.

Assume, in the system illustrated, there is a sudden increased load demand. The'line voltage will begin to fall and the condensers 7 and 8 will have ahigher countervoltage and consequently draw aleading current the magnitude of which will depend, among other things, on the fall in line voltage. The magnitude of this current, as has been pointed out, will be suflicient to prevent a decrease in line voltage to the point of instability. This maintenance of the line voltage is supplemented by the regulator 11 which increases the current in field winding 12 of condenser 7 In like manner the regulator 14. provides for an increase of current in the field 15 of condenser 8.

In the resent system the inherent regulating action of the synchronous condensers enters into the o eration of the system as a material factor because the reactive power added to the systemfor a slight chan e in line voltage is of suificient magnitu e to prevent an abrupt chan e in line voltage and when the regulator nations the voltage is brought back to a predetermined value. mits operation closer to the maximum power limit of a given line arid provides for a power transfer greatly in excess of systems depending solely on voltage regulator control.

What I claim as new and desire to secure by Letters Patent of the United States, is: 1. In a high-Volta e electrical power transmission system, t e combination of a Therefore, the present system persource of alternating-current supply, a receivin circuit, a transmission line connecting said source of supply and said receiving circuit, means comprising a synchronous phase modifier with a highly saturated field structure connected to said transmission line,

a regulator for automatically regulating the field excitation of said phase modifier in accordance with voltage variations in the line, said phase modifier being so saturated that upon sudden application of load and consequent decrease in line voltage corrective reactive power of sufficient magnitude is added to the system to prevent a material drop in voltage, whereby the system may be operated closer to its maximum power limit.

2. In a high-voltage electrical power transmission system, the combination of a source of alternating-current supply, a receiving circuit, a transmission line connecting said source of supply and said receiving circuit, a synchronous condenser with highly saturated field poles connected to the line at a point intermediate the su ply and renected to the line at a point a'd acent the receiving circuit, a regulator for each synchronous condenser automatically regulating the field excitation thereof in accordance with the variations in line voltage at the respective points of connection, said s nchronous condensers being so saturated t at upon sudden increase in power'demand corrective reactive power of sufficient magnitude is added to the system to prevent the line voltage from dropping to a value where the line is unstable, whereby the system may be operated closer to its maximum power limit. i

'3. In a high-Volta e electrical power transmission system, t e combination of a llO source of alternating-current energy supply, a receiving circuit, a transmission line connecting said source of supply and said receiving circuit, a s nchronous condenser with highly saturate field poles connected in parallel with said receiving circuit, a regulator for automatically regulating the field excitation of said synchronous condenser inaccordance with variations in reto maintain the voltage above a" which the line is unstable. 1 I

4. Ina high-Volta e electrical power" transmission system, t e combination of a source of alternating-current supply, a re-.

ceiver voltage, said synchronous condenser being so saturated that uponsudden application of load corrective reactive power of sufiicient magnitude is added to the system,- during the interval required for the regulatorjo function to restore the line voltage, value at ceiving circuit, a transmission line connecting said source of supply and said receiving circuit, a synchronous condenser with. highly'saturated field poles connected to the line at a point intermediate the supply and receiving circuit, a regulator for automatically regulating the field excitation of said synchronous condenser in accordance with EDITH CLARKE. 

